1. Field of the Invention
The present invention related to a self-ligating bracket for use in orthodontics.
2. Description of Related Art
A bracket of this kind has been known from U.S. Pat. No. 5,906,486. The known bracket comprises a base the bottom of which is prepared for being glued onto a tooth. The base carries a support which has a surface area generally smaller than the base. An occlusal wall and a gingival wall extending from the support include between them a groove which is open in the labial direction and which extends continuously from the mesial to the distal end, separating the occlusal wall and the gingival wall one from the other. In German technical language, just as in the English language, the groove is also described as “slot”. It serves to receive an arch wire which usually runs through a succession of brackets mounted on a series of neighboring teeth. By drawing or twisting the wire a pre-stress can be produced in the wire which will be transmitted by the arch wire to the brackets, and from the latter to one or more teeth for the purpose of modifying the orientation of the teeth.
The occlusal wall and the gingival wall of the known bracket are each provided with one or two ligature wings on which ligature wires can be mounted.
In order to secure the position of the arch wire in the slot of the bracket, the known bracket is provided with a resilient clip comprising a labial leg and a lingual leg that are connected one with the other by a section arranged on the occlusal side. The clip is captivated on the bracket. The bracket is provided for this purpose with a slot which extends continuously through the support, from the occlusal to the gingival end, and which is defined by a wide lingual surface, a wide labial surface, and two narrow mesial and distal surfaces extending at a right angle relative to the first-mentioned surfaces. The lingual leg of the clip is received in that slot. The clip can be displaced between a closed position in which the labial leg extends into a recess in the gingival wall of the bracket and an open position in which the tip of the labial leg rests on the occlusal wall. In the open position, an arch wire can be fitted in the slot or can be removed from the slot. In the closed position, the labial leg of the clip closes the slot in the labial direction and is in resilient contact with the arch wire in order to press it down toward the bottom of the groove. In the event the arch wire exerts upon the labial leg of the clip a force that exceeds the restoring force of the clip, the recess in the gingival wall is limited by a labial stop which will be contacted by the labial leg of the clip when a sufficiently high force is exerted on the labial leg by the arch wire. Further, the stop in the gingival wall of the bracket limits the maximum dimension of the arch wire in the lingual-to-labial direction. In the closed position, the clip is held by the fact that the labial leg, when being displaced toward the closed position, will come into resilient contact with the occlusal wall, and can be transferred from its closed position to its open position only by bending it up elastically. In the open position, the clip of the known bracket can be held by an arrangement where the tip of the labial leg of the clip springs resiliently into a recess provided on the labial end of the occlusal wall.
For moving the clip from its closed position to its open position, the labial leg of the clip of the known bracket is provided with a hole that can be engaged by a pin. The pin can be used as a lever by means of which the clip can be moved from its closed position to its open position. That hole is connected with disadvantages. On the one hand, it weakens the clip. This disadvantage cannot be remedied by an increase in size of the clip because there exists a simultaneous demand that the bracket should be as small as possible. On the other hand, food particles may easily get into the space between the clip and the occlusal wall, through the hole in the clip, and may even be compacted by the chewing process. The food particles practically cannot be removed by usual tooth-cleaning methods, which is detrimental in terms of oral hygiene.
In order to prevent the clip from getting lost during transfer from the closed position to the open position, the tip of the lingual leg of the clip, being located outside of the slot, is provided with an embossed mark that will fit through the slot in which the lingual leg of the clip is received only if it is deformed elastically. The force required for sliding the embossed tip of the lingual leg of the clip through the slot may, however, very well be applied when transferring the clip to its open position so that there actually exists a risk of the clip getting lost or of the patient swallowing it.
Now, it is the object of the present invention to open up a way how the risk of the clip getting lost unintentionally can be reduced or avoided without much expense.
This object is achieved by a the inventive bracket.
The self-ligating bracket for use in orthodontics according to the invention comprises
a base;
a support arranged on the base;
an occlusal wall with at least one occlusal ligature wing extending from the support;
a gingival wall with at least one gingival ligature wing extending from the support;
a first slot separating the occlusal wall and the gingival wall one from the other and extending continuously in the mesial-to-distal direction;
a second slot which extends continuously through the support in the gingival-to-occlusal direction, and which is limited by a lingual surface and by a labial surface; and
a resilient clip having a labial leg and a lingual leg that are connected one to the other by an occlusal section;
the lingual leg being received in the slot and being arranged for displacement in the slot in the gingival-to-occlusal direction between a closed position in which the labial leg extends into a recess in the gingival wall and an open position of the clip in which the tip of the labial leg rests on the occlusal wall.
A tongue directed toward the occlusal wall of the bracket is cut out from the lingual leg of the clip and is bent off in the labial direction so that an acute angle is enclosed between the tongue and the lingual leg of the clip.
Such a tongue protects the clip from getting lost during transfer to its open position because, being directed toward the occlusal wall, the tongue will hit against the occlusal wall and be blocked when an attempt is made to move the clip beyond its open position during transfer to its open position from its closed position. Moving the lingual leg of the clip completely out of the second slot, thereby fully detaching the clip from the bracket, will be possible only by pushing the tongue back into the recess in the lingual leg of the clip and simultaneously pressing on the gingival end of the that leg of the clip, or pulling at the occlusal section of the clip. This cannot happen unintentionally. For pressing down the tongue, a tool, for example a pin or a scaler, must be inserted into the second slot from the labial direction. When sliding the clip onto the bracket the tongue will not be felt as an obstacle because it is introduced into the second slot with that end first which foots on the clip, being thus pushed into the recess in the lingual leg of the clip automatically. Consequently, the lingual leg of the clip can be introduced into the second slot of the bracket even more easily than the embossed lingual leg of the clip of the self-ligating bracket known from U.S. Pat. No. 5,906,486 A.
The labial surface, which delimits the second slot, is removed or interrupted in the area of the gingival wall of the bracket. This leaves room for the tongue which is to be displaced by the lingual leg of the clip. And it provides the further advantage that it will be easier for a tool, for example a scaler, to act on the gingival end of the lingual leg of the clip for displacing it from its closed position to its open position and to follow the gingival end of the lingual leg of the clip, as the tool used for displacing the clip can be moved along the area where the labial surface delimiting the second slot has been removed or interrupted.
Preferably, the labial surface delimiting the second slot is removed or interrupted also in the area of the groove. There is then ample room for the tongue also below the bottom of the first slot, and according to an additional advantage it is then easily possible to act on the lingual leg of the clip, and to press down the tongue, through the groove from the labial direction. At the same time, that feature reduces friction between the bottom of the first slot and an arch wire in the first slot.
According to an advantageous further development of the intention, the lingual surface, which delimits the second slot, projects beyond the tip of the lingual leg of the clip in any position of the clip, and a positioning aid for a tool is provided at the gingival end and/or before the gingival end of the lingual leg of the clip, by means of which the clip can be displaced from the closed position to the open position by pressure exerted on the gingival end of its lingual leg. This greatly facilitates transfer of the clip from its closed position to its open position the latter being definitely reached when the tongue hits against the occlusal wall.
The described further development provides substantial additional advantages:
                No hole in the labial leg of the clip is needed for displacing the clip from its closed position to its open position. This considerably reduces the risk of food particles being pushed into the area between the clip and the bracket, and being compacted in this space, compared with the prior art.        Oral hygiene is improved.        As there is no hole in the labial leg of the clip, the latter is felt much less as a nuisance and looks more attractive.        Although the position of the gingival end of the lingual leg of the clip is visible in the mouth either not at all or only with difficulty, the clip may easily be displaced from the closed position to the open position by exerting pressure on the gingival end of its lingual leg the point at the gingival end of the lingual leg of the clip, where the pressure is to be applied, can be felt and found even blind using the positioning aid.        Contrary to the hole in the labial leg of the clip provided according to the invention, the positioning aid provided on the gingival end or in the vicinity of the gingival end of the lingual leg of the clip does not weaken the clip and its restoring force.        The lingual leg of the clip cannot evade the pressure exerted on its gingival end because it is guided straight in the second slot in which it is fitted. This would be different for pressure acting on the labial leg of the clip, as in this case the clip might be damaged, or the tool may slip off and may injure the patient.        It is not necessary to procure a special tool for displacing the clip to its open position. Suitable tools are available in any orthodontic practice in great number, for example in the form of scalers.        The positioning aid reduces the risk of the tool slipping off the gingival end of the lingual leg of the clip when pressure is applied on the gingival end.        
A suitable positioning aid may consist of a notch in the gingival end of the lingual leg of the clip. The notch does not weaken the restoring force of the clip and is easy to clean. It can be found by moving the tip of a tool, for example the tip of a scaler, across the base of the bracket, along the edge of the support. One then automatically hits upon that section of the base that projects beyond the tip of the lingual leg of the clip, up to which the lingual surface of the second slot extends. The tool then hits upon the end of the lingual leg of the clip, with its tip automatically entering the notch, so that it can then exert the pressure necessary for displacing the clip from its closed position to its open position.
According to another possibility, a positioning aid consists in a groove, extending in the gingival-to-occlusal direction, in that section of the lingual surface delimiting the second slot that projects beyond the clip. Again, this groove will be necessarily found when the tip of a tool is moved across the base of the bracket along the edge of the support. The fact that the groove has been reached is easily felt. Once the tool is in the groove it can easily be moved in the groove up to the gingival end of the lingual leg of the clip, for displacing the clip to its open position.
The two possibilities may also be combined. Both possibilities are based on the idea to provide a recess, that can be felt using a tool, at a point where pressure is to be applied on the gingival end of the lingual end of the clip.
Preferably, the groove gets narrower from its gingival to its occlusal end and leads to the center of the edge on the gingival end of the lingual leg of the clip. This facilitates the process of finding the groove and of centering the tool on the point best suited for displacing the clip. The groove should extend at least up to the lingual leg of the clip in its closed position. Preferably, it extends still further up to a point below the lingual leg of the clip so that the tool can be guided in the groove over the entire length of displacement of the clip from its closed position to its open position. This further development recommends itself especially in cases where no notch is provided on the gingival end of the lingual leg of the clip.
Preferably, the groove ends at a stop which, with the clip in the closed position, comes to lie below the lingual leg of the clip, at a spacing from the tip of the lingual leg of the clip. Preferably, the stop is located at the point where the tip of the lingual leg of the clip lies in the open position of the clip. This ensures that the movement of the tool will automatically be stopped once the open position of the clip is reached because the tool will then hit against the stop. However, instead of being transmitted to the delicate clip, the peak force will be transmitted to the solid bracket in this case while the clip will be protected.
Preferably, the groove extends in the base of the bracket, at least in part. This is favorable with a view to achieving a small overall height of the bracket which in turn improves the wearing comfort in the mouth. To further the small overall height, the bracket preferably is formed as a single piece. In the case of metal brackets according to the prior art the base frequently is made as a separate part and is connected with the support of the bracket by welding in a second step. According to the invention it is, however, preferred to form the bracket as a single piece, especially by metal injection molding (MIM), a method for the powder-metallurgical production of metallic molded parts related to the injection molding process. With the aid of that method, it is possible to simultaneously form alternately oriented undercut projections on the lower surface of the base of the bracket, which when the bracket is glued onto a tooth lead to clearly improved adhesion of the bracket to the tooth compared with conventional brackets where a wire grating is welded to the lower surface of the base of the bracket. The bonding strength that can be achieved with the aid of the undercut projections is higher by approximately 30% than with brackets provided with a wire grating on their bottom surface. As to the configuration of such undercut projections on the lower surface of the base, reference is made to WO 96/09015 A1. The higher bonding strength achievable in this case is of particular advantage in the case of the present invention because in reduces the risk of the bracket being detached from the tooth by the force applied for displacing the clip from its closed position to its open position and by the tool used for this purpose hitting against the bracket.